1. Field of the Invention
This invention relates to a diaphragm device to be used for a camera or other optical apparatus and more particularly to a diaphragm device arranged to have the aperture thereof electrically controlled with a motor or the like used as drive source.
2. Description of the Prior Art
Control methods for determining exposure conditions which are important for photographing include an aperture preference type and the shutter time preference type. In both of these types, a photographic computation system is arranged to perform electric control according to various factors which give exposure conditions including the brightness of an object to be photographed, the sensitivity of film, a shutter time value, an aperture value, etc.
The control systems of cameras are at present and will be in future arranged to perform such electric control as a prerequisite for an increased speed and a higher accuracy of the control. To keep up with such electric control arrangement on the side of the camera, photo-taking lenses also have been either arranged to include an automatic focusing device or arranged in the form of a zoom lens to be driven by means of a motor. In the case of the photo-taking lens of the type having a motor included therein, a conventional discrete motor has been mounted on the photo-taking lens with the rotating shaft of the motor arranged to be linked to a movable member of the photo-taking lens via a gear train or the like. This arrangement of the prior art, therefore, has hardly permitted reduction in size of the lens.
Meanwhile, there has been proposed a diaphragm blade driving control system in which an electromagnetic driving device is included in a diaphragm device and is arranged to drive diaphragm blades by means of an electromagnetic force as disclosed, for example, in U.S. Pat. No. 3,687,042. In the diaphragm device of the prior art, however, the component parts of the diaphragm device and those of the electromagnetic driving device are arranged separately from each other and are not arranged in common. As a result, the diaphragm device as a whole becomes complex in structure and large in size.
Further, there has recently been proposed a method in which a diaphragm device is arranged to be operated by a hollow motor formed into a hollow shape similar to the shape of the diaphragm body. This method certainly permits reduction in the outer diameter of the lens. However, the connection part between the motor and the diaphragm body requires complex arrangement. Another shortcoming of the method lies either in poor responsivity of diaphragm blades due to insufficient performance of the motor or a high cost of the hollow motor.